1. Field of the Invention
The invention relates to a device for high-precision generation and measurement of forces and displacements.
2. Description of the Prior Art
High-precision generation and measurement of forces and displacements along an axis are generally used in the production of nano-indenters and scratch or wear testers. Forces and displacements in such devices are generated in different ways, according to the state of the art, whereby as a rule, only great rigidity of the moved shaft in the movement direction is a matter of concern.
Force and/or displacement can be generated and/or measured electrically (for example, electrostatically or capacitatively), magnetically, mechanically, or by means of a combination of the aforementioned methods. Simple methods for determining displacements and forces, such as optical reading of the displacement of a glass scale, and the use of a force measurement cell are described in the U.S. Pat. No. 5,616,857. Such methods, however, are only suitable for sufficiently large paths and forces. Another method is described in DE 3738106, wherein the force is generated by means of the current flowing through a coil which is situated in a field produced by permanent magnets. In this connection, the electric current is a measure of the force that is generated. However, the reproducibility is dependent on the constancy of the magnetic field of the permanent magnets.
A magnetic system is also described in DE 3408554. This system is in the form of a rotary magnet, which moves a lever arm that transfers a force to a substrate. Again, the electric current through the magnet serves as a measure of the force. In this system, however, the bearings can influence the accuracy and reproducibility of the force transfer.
DE 3128537 also describes a system wherein force is generated by way of a lever. A lever arm is moved using a cam. The determination of the transferred force takes place by way of an elongation measurement strip that is attached to an elastic part of the force transfer arm, while the path measurement takes place by means of a sensor on the shaft of the measurement device. Elongation measurement strips, however, have a poor signal/noise ratio for small signals. Significantly greater precision is possible using capacitative measurements, as they are described, for example, in U.S. Pat. Nos. 5,576,483 and 5,661,235. As described in these references, generation and measurement of path and force take place by way of electric voltages. In particular, the change in capacitance of a capacitor at a variable distance between its plates, or the change in the distance between the plates with a variable applied voltage is utilized.
According to U.S. Pat. No. 5,661,235, this system can be utilized for detecting forces and displacements in multiple directions. However, the forces that can be generated are on the order of 10 mN, and this is a significant disadvantage. Furthermore, the work is carried out using voltages of more than 100 V, which presents the risk of electric blowout. This would cause the force generation to become unusable. Furthermore, the suspension of the substrate holder must be electrically insulating, so that the internally used voltage does not reach the outside.
U.S. Pat. No. 5,067,346 describes the generation and measurement of forces and displacements by means of leaf springs that are clamped in on one side and not biased. Here, a disadvantage is the low rigidity in a direction perpendicular to the force and displacement being generated.
DE 37 21 525 A1 describes a microhardness testing device wherein a force-transferring shaft is attached to two membrane springs disposed in a force measurement housing. The membrane springs are perforated, held at their circumference and configured to be wave-shaped at their free side edges The shaft is movable and guided in the axial direction.
DE 42 20 510 A1 describes a device for setting a measurement tip onto a substrate, wherein the measurement tip is disposed on a vertically movable carrier. The carrier is clamped in place between two leaf springs, which are attached to a base body. A similar device is described in EP 1092142 B1, wherein a penetration body is disposed to be movable in one degree of freedom, by way of a penetration body holder attached to leaf springs.
In the case of the three solutions described above; however, a defined bias force of the membrane springs or leaf springs is not adjustable, and thereby each of the systems demonstrates insufficient rigidity.